package org.opentrafficsim.base.geometry;
   
   import java.util.Iterator;
   import java.util.NoSuchElementException;
   
   import org.djutils.draw.bounds.Bounds2d;
   import org.djutils.draw.line.Polygon2d;
   import org.djutils.draw.point.Point2d;
   import org.djutils.exceptions.Throw;
  
  /**
   * Shape defined by a circle.
   * <p>
   * Copyright (c) 2024-2024 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
   * </p>
   * @author <a href="https://github.com/wjschakel">Wouter Schakel</a>
   */
  public abstract class CircleShape implements OtsShape
  {
  
      /** Radius. */
      private final double radius;
  
      /** Number of line segments in polygon representation. */
      private final int polygonSegments;
  
      /** Polygon representation. */
      private Polygon2d polygon;
  
      /** Bounds. */
      private final Bounds2d bounds;
  
      /**
       * Constructor.
       * @param radius radius.
       */
      public CircleShape(final double radius)
      {
          this(radius, DEFAULT_POLYGON_SEGMENTS);
      }
  
      /**
       * Constructor.
       * @param radius radius.
       * @param polygonSegments number of segments in polygon representation.
       */
      public CircleShape(final double radius, final int polygonSegments)
      {
          Throw.whenNull(radius, "Radius must not be null.");
          Throw.when(radius <= 0.0, IllegalArgumentException.class, "Radius must be above 0.0.");
          this.radius = radius;
          this.polygonSegments = polygonSegments;
          this.bounds = new Bounds2d(2 * radius, 2 * radius);
      }
  
      @Override
      public Bounds2d getRelativeBounds()
      {
          return this.bounds;
      }
  
      @Override
      public double signedDistance(final Point2d point)
      {
          return Math.hypot(point.x, point.y) - this.radius;
      }
  
      @Override
      public Polygon2d getRelativeContour()
      {
          if (this.polygon == null)
          {
              if (this.radius == 0.0)
              {
                  this.polygon = new Polygon2d(new double[] {0.0}, new double[] {0.0});
              }
              else
              {
                  this.polygon = new Polygon2d(new Iterator<Point2d>()
                  {
                      /** Step. */
                      private int step = 0;
  
                      @Override
                      public boolean hasNext()
                      {
                          return this.step <= CircleShape.this.polygonSegments;
                      }
  
                      @Override
                      public Point2d next()
                      {
                          Throw.when(!hasNext(), NoSuchElementException.class, "Iterator has no more elements.");
                          // at full circle (this.step == polygonSegments), make sure end point is exactly the same as the start
                          // point
                          double ang = this.step == CircleShape.this.polygonSegments ? 0.0
                                  : (2.0 * Math.PI * this.step) / CircleShape.this.polygonSegments;
                          this.step++;
                         return new Point2d(Math.cos(ang) * CircleShape.this.radius, Math.sin(ang) * CircleShape.this.radius);
                     }
                 });
             }
         }
         return this.polygon;
     }
 
     @Override
     public String toString()
     {
         return "CircleShape [radius=" + this.radius + "]";
     }
 
 }